1. Field of the Invention
The present invention relates generally to a method of manufacturing a wiring substrate used suitably for an electron source substrate and an image forming apparatus provided with an electron source substrate. The present invention also relates to a wiring substrate manufactured by the above-mentioned manufacturing method, an electron source substrate with the wiring substrate, and an image forming apparatus with the electron source substrate.
2. Related Background Art
Generally, a so-called xe2x80x9ccathode-ray tube (CRT)xe2x80x9d has been known widely as an image forming apparatus used for image display on a TV, a personal computer monitor, or the like.
Recently, cathode-ray tubes having a display screen with a size exceeding 30 inches have been introduced. In a cathode-ray tube, however, in order to increase the size of its display screen, it is necessary to increase its depth in accordance with the increase in size of the screen and in turn its weight increases. Hence, such a cathode-ray tube can hardly be said to be suitable for satisfying consumers"" wish to watch powerful images on a larger screen since it requires a lager installation space.
Hence, the advent of a low-power-consumption flat image display device that is thin and light has been expected so that such a unit can be hung on a wall instead of a large and heavy cathode-ray tube (CRT).
Liquid crystal displays (LCD) have been researched and developed actively as flat image display devices. However, LCDs are not of a self-emission type. Hence, a light source called a xe2x80x9cbacklightxe2x80x9d is required and most of the power to be consumed is used by this backlight. In addition, there still remains a problem of difficulty in increasing the screen size to over 30 inches.
In place of LCDs with such problems as described above, a self-emission-type thin image forming apparatus has been receiving attention. Examples of such a display unit include a flat image forming apparatus in which fluorescent substances are irradiated with electrons emitted from electron emission devices to be excited and thereby to emit light.
In increasing the size of such an image forming apparatus, it also is suitable from the viewpoint of reduction in cost and resistance to form thick-film wirings by a printing process as wirings for sending a signal to each electron emission device.
However, the following problem is caused when such wirings as described above are formed.
Preferably, the above-mentioned wirings are formed to intersect with each other in a matrix form so as to address the electron emission devices individually. In other words, there are crossing points at which a first wiring and a second wiring intersect (are laminated) with each other. At such a crossing point, an insulating layer (an interlayer insulating layer) for electrically insulating the respective wirings from each other is placed between the first and second wirings. Such a wiring structure is disclosed in, for example, Japanese Patent Application Laid-open Nos. 2000-244122, 2000-311600 and 09-283061.
At the crossing point where the first and second wirings intersect with each other, it is required to secure the electrical insulation between the first and second wirings. In some cases, however, pinholes may be produced in the interlayer insulating layer depending on the manufacturing method or the like. Consequently, a defect of short-circuit between the wirings has been a problem. Furthermore, in order to avoid this, an interlayer insulating layer may be formed of a plurality of layers superimposed on each other. However, this may not be sufficiently effective for avoiding the production of pinholes in some cases.
The present invention is intended to solve the above-mentioned problem in conventional way. It is an object of the present invention to improve the method of forming a plurality of insulating layers superimposed on each other and thereby to provide a method of manufacturing a wiring substrate that can prevent a defect of short-circuit between wirings that are laminated with each other to be formed, and a wiring substrate that has no defect of short-circuit and is excellent in electrical insulation between wirings.
Another object of the present invention is to provide a method of manufacturing an electron source substrate that can prevent a defect of short-circuit between wirings that are laminated with each other to be formed and to provide an electron source substrate that has no defect of short-circuit and is excellent in electrical insulation between wirings.
Further, still another object of the present invention is to provide an image forming apparatus that has no defect of short-circuit between wirings and that is superior in reliance and to provide a method of manufacturing such an image forming apparatus.
In order to solve the above-mentioned objects, according to the present invention, there is provided a method of manufacturing a wiring substrate on which first and second wirings intersect with each other at a crossing point through an insulating layer, the method being characterized by comprising the steps of:
providing a wiring pattern on the substrate with a conductive paste and baking the wiring pattern of the conductive paste to form the first wiring (or providing a wiring pattern and baking the wiring pattern to form the first wiring the sidewall of which is undercut);
coating part of the first wiring at the crossing point with an insulating paste and baking the insulating paste to form a first insulating layer, the thickness of the insulating layer formed adjacent to sidewalls of the crossing point is substantially equal to the height of the first wiring;
forming a second insulating layer on the first insulating layer coating the crossing point; and
forming a second wiring which crosses over the second insulating layer to intersect with the first wiring.
Further, there is provided a method of manufacturing a substrate on which a first and second wirings intersect with each other at a crossing point, comprising the steps of:
providing a wiring pattern on the substrate with a conductive paste and baking the wiring pattern of the conductive paste to form the first wiring;
coating part of the first wiring at the crossing point with an insulating paste and baking the insulating paste to form a first insulating layer, the coating thickness of the insulating paste being controlled so that the height of the first insulating layer formed adjacent to sidewalls of the first wiring at the crossing point is substantially equal to the height of the first wiring;
forming a second insulating layer on the first insulating layer and the first wiring at the crossing point; and
forming a second wiring which crosses over the second insulating layer to intersect with the first wiring.
Further, there is provided a method of manufacturing an electron source substrate on which a first and second wirings connected to an electron emission device intersect with each other at a crossing point, comprising the steps of:
providing a wiring pattern on the substrate and baking the wiring pattern to form the first wiring the sidewall of which is undercut;
coating part of the first wiring at the crossing point with an insulating paste and baking the insulating paste to form a first insulating layer, the coating thickness of the insulating paste being controlled so that the height of the first insulating layer formed adjacent to sidewalls of the first wiring at the crossing point is substantially equal to the height of the first wiring;
forming a second insulating layer on the first insulating layer and the first wiring at the crossing point;
forming a second wiring which crosses over the second insulating layer to intersect with the first wiring; and
forming the electron emission device so as to be connected to said first and second wirings.
Further, an electron source substrate according to the present invention is characterized in that the electron source substrate is manufactured by the above-mentioned manufacturing method.
Further, according to the present invention, there is provided an image forming apparatus, characterized in that the apparatus is manufactured by the above-mentioned manufacturing method.